1. Field of the Invention
This invention relates to a process for enhancing the recovery of petroleum and bitumen from subterranean strata and petroliferous rocks or sands. More specifically, it relates to new and improved aqueous flooding processes wherein the improvement comprises the utilization of a thin film spreading agent composition of a polyether polyol which facilitates the displacement of petroleum and bitumen from the source rock.
2. Description of the Prior Art
It has long been known that the natural forces operating to cause flow of oil from source rocks into bore holes penetrating the rock are relatively inefficient in producing the oil. After the completion of such "primary" production, as much as 60% to 95% of the original oil in place may remain in the reservoir stratum.
For this reason, so-called "secondary" and "tertiary" recovery processes are usually applied to the reservoir at some point. Such processes include steam injection to provide additional reservoir energy for subsequent oil production and numerous other recovery methods which have been proposed wherein various fluids are injected into the oil-bearing formation to effect removal and recovery of additional oil from treated wells or from adjacent wells communicating with the reservoir. Such displacement methods are generally referred to as "flooding" and have utilized steam, water, brines, gas, caustic solutions, acidic solutions, aqueous solutions of detergents, high viscosity aqueous solutions of very high molecular weight polymers, oil solutions of detergents, micellar solutions, emulsions, liquified carbon dioxide and combinations of such methods. In some instances, one fluid may be injected for a time and is then followed by another and perhaps less costly fluid, such as water or brine. All such procedures are aimed at removing petroleum trapped in minute pores of the reservoir rock.
Removal of petroleum from its source rock is believed to be a complex process involving the flow of two or more phases through a permeable solid phase. Many variables affect the results. For example, pore size in the rocks, viscosity of fluids, temperature, pressure, wettability characteristics of the rock, the composition of the oil phase and numerous other properties all apparently play a part in the dynamics of petroleum production.
Much of the oil left in the rock formation during primary production appears to be trapped by forces of adhesion between oil and rock. Although not fully understood, most reservoir rocks appear to be "preferentially" wet by water, meaning that the contact angle between water and rock, measured through the water phase, is smaller than the contact angle between crude oil and rock, similarly measured. It is believed that the polar constituents contained in most crude petroleum oils, such as asphaltenes and other complex compounds, become absorbed on the polar rock surfaces to form thick, viscous, hydrophobic films which cause the rock to be wettable or partially wettable by the oil, prevent the close approach of and wetting by any aqueous phases and hinder the displacement and flow of the oil. Even in the presence of interstitial (connate) water or of injected aqueous fluids, only limited water wetting of the formation with displacement of the oil is effected.
Micellar solution flooding systems which are miscible with the petroleum, all of its dissolved components and water, were first disclosed and proposed for oil recovery in U.S. Pat. No. 2,356,205, dated Aug. 22, 1944, to Chas. M. Blair, Jr., and Sears Lehmann, Jr., entitled "Process For Increasing Productivity Of Subterranean Oil-Bearing Strata", the disclosure of which is herein incorporated by reference. These systems are capable of dissolving and removing such trapped oil as they can contact, but have not yet proven to be generally feasible because of the high cost of chemicals, solvents and hydrotropic agents involved.
Aqueous flooding fluids containing acids, bases or detergent solutes have been employed to improve oil recovery by lowering oil-water interfacial tension sufficiently to lessen back pressure from dynamic surface and interfacial tension (Jamin) effects or to bring about emulsification of oil in the aqueous fluid, but with only limited improvement over the results of ordinary water flooding.
None of these methods has clearly attempted to effect more complete water wetting of the formation by chemical means. Indeed, the use of water- or brine-soluble surfactants, such as detergents, for decreasing oil-water interfacial tension are generally ineffective in decreasing oil wetting or, alternatively, increasing water wetting of highly polar surfaces. Classical wetting theory shows quite generally that the work of adhesion for displacement of oil by water on a rock surface is decreased by lowering the oil/water interfacial tension and, as a consequence, the tendency of the water to displace oil is actually decreased.
Indirectly, aqueous caustic may reduce the oil wettability of rock by reaction with crude oil constituents and reduction of their oil wetting action. However, this method typically requires from 1/2% to 3% of caustic, and sometimes as much as 15%, to reduce the oil-wetting ability of the petroleum. Such high concentrations are costly and, in addition, bring about reactions with injected water or interstitial brine to form plugging precipitates of inorganic compounds such as calcium carbonate, strontium carbonate and magnesium hydroxide, thus stopping or greatly reducing the fluid injection process.